Hydrotreating is a commonly used process in many modern refineries, in which hydrogen is contacted in the presence of a catalyst with a hydrocarbonaceous feedstock to remove impurities, including oxygen, nitrogen, sulfur, and unsaturated hydrocarbons. Consequently, hydrotreating is frequently employed to reduce the sulfur content from refined intermediates and is also commonly referred to as hydrodesulfurization. Hydrodesulfurization is typically used within a refinery in combination with processes including feed pretreatment of catalytic reformers, catalytic crackers, and hydrocrackers, product quality improvement for naphtha, diesel, jet, heating oil and residues, saturation of olefins, and polycyclic aromatics. There are numerous hydrotreating configurations and processes known in the art, and continuous efforts to reduce energy and material consumption led to integration of hydrotreating reactors in various processes.
For example, in one integration concept, a hydrotreater is combined with a hydrocracker as disclosed in U.S. Pat. No. 3,328,290 to Hengstebeck that describes a two-stage hydrocracking process wherein fresh feed is combined with effluent from the hydrocracking stage and the combined streams are then introduced into a hydrotreating stage. A higher-boiling fraction is then separated from the hydrotreater effluent and fractionated to produce a light product and a heavier-bottoms stream, which is then recycled with hydrogen-containing gas back to the hydrocracking stage.
Another example U.S. Pat. No. 6,235,190 to Bertram describes an integrated hydrotreating and hydrocracking process in which two hydrotreating catalysts of different activity are operated in series to provide improved products that are then subjected to a hydrocracking process to convert the hydrotreated effluent to lighter products with a reduced aromatic hydrocarbon content.
In a further example, as described in U.S. Pat. No. 6,261,441 to Gentry et al., a combined hydrotreating/hydrocracking process is described in which a hydrocracking stage is followed by a hydrodewaxing stage with a single feed and a bottoms fraction recycle to produce a naphtha product, a distillate boiling above the naphtha range, and a lubricant.
In yet another system, as described in U.S. Pat. No. 6,328,879 to Kalnes, two independent feedstocks are hydrocracked in a catalytic hydrocracking process that employs a hydrocracking zone, a hydrotreating zone, and a high pressure product stripper to produce various products from two feedstocks, wherein the products have a lower boiling point range than the feedatocks.
Alternatively, more than one hydrotreater reactor, and or catalyst beds may be employed for catalytic hydrogenation as described in U.S. Pat. No. 3,537,981 to Parker, or U.S. Pat. No. 6,103,105 to Cooper. While Parker's process employs a first hydrotreating reactor coupled to a separator that is in series with a second hydrotreating reactor, Cooper et al. employ two serially connected hydrotreating catalyst beds without the use of a separator. However, both Coopers and Parkers configuration are typically limited to only a single feedstock. Alternatively, as described in U.S. Pat. No. 5,958,218 to Hunter, two hydrocarbon feedstocks are hydrotreated in parallel while hydrogen flows in series between the reactors. While Hunters configuration allows hydrotreating of two at least somewhat different feedstocks, the catalytic reactors will generally operate at different hydrogen partial pressures. Consequently, the balance of the feedstocks will have to be properly balanced with the particular hydrogen partial pressures to yield the desired products.
Thus, although many integrated processes have provided at least some advantage over other known conligurations and methods, such configurations and methods are frequently limited to processes involving hydrocracking, or hydrotreating of a single boiling range (e.g., naphtha, diesel, gasoil, resid) feedetock. Consequently, all or almost all of the known hydrotreating processes require separate plants where more than one feedstock is employed. Therefore, there is still a need to provide improved configurations and methods for hydrotreating of petroleum products.